It is interesting to note that in a variety of electron systems collinear dynamics is known to speed up quasiparticle decays rather than slow them down. Speed-up arises because collinear scattering, by allowing particles to travel side by side for a longer time and thereby interact more strongly, enhances the effective interactions and shortens lifetimes. This behavior is well documented, e.g., for electrons in Dirac bands, where collinear processes arising from linear band dispersion impact carrier photoexcitation cascade and hot carrier lifetimes[1]}, [2]}, [3]}, [4]}, [5]}, [6]}.
Different behavior in our problem originates from the delicate interplay of collinear scattering and phase space constraints. These effects dominate at a 2D Fermi surface but are of little importance for highly excited states in Dirac bands.
